Download D1, PPID: An Up-to-Date Review of Equine Cushing`s Disease

Melinda Freckleton, DVM
Haymarket Veterinary Service
Haymarket, VA
703-754-3309
540-272-9319
[email protected]
PPID: An up to date look at Equine Cushing's Disease
Part 1: What is ppid? Which horses get it? What are the
signs?
Does your equine roster include short, sturdy, calm, fuel efficient breeds like Morgans,
Arabians, Mustangs, Halflingers, Fjords, or ponies of any kind? This includes cross
breeds! Does your center use horses of any breed that are over the age of 15 years? If
you answered yes, then there is a high risk that you have horses with Pars Pituitary
Intermedius Dysfunction (PPID), also known as Equine Cushing's Disease. Recent
research has deepened our knowledge of this disease, and has allowed great
advancement in diagnosis and treatment. Early diagnosis and treatment can greatly
improve the health of these horses, prevent equine disability, and extend the happy
working career length of your invaluable horses!
As recently as 15 years ago this was considered a disease of only the very oldest
horses, and we thought most of the horses with this disease had a long curly coat, huge
cresty neck, obesity and, most likely, laminitis. Now we know that this is a description of
the very end stage cases. With our deeper understanding, we now know that in most
breeds onset can occur in the teenage years. And in the breeds listed above the onset
can be as early as 6-8 year of age. This covers a huge percentage of horses used in
Equine Assisted Activities and Therapy (EAAT)!
How does undiagnosed and untreated PPID affect a EAAT organization? With
increased veterinary expenses, increased horse care burdens for your staff or
volunteers, possible equine disability, or even death of your horses, this is not a good
outcome. Early detection will greatly improve the health, welfare and performance of
your hard working EAAT horses!
As the name PPID suggests, this is a disease of the pituitary gland of horses. The
pituitary is located in the skull just under the brain. Due to degeneration of nerves that
connect the hypothalamus (a part of the brain) to the pars Intermedius of the pituitary an
excessive amount of a hormone called ACTH (adrenocorticotropic hormone) is secreted
from this part of the pituitary into the blood stream. This hormone tells the adrenal
glands to secrete an excessive amount of cortisol. Cortisol is the body's hormone of
chronic stress, so day after day and week after week the adrenals are telling all the
other systems of the body to essentially man the battle stations! The effects are much
the same as actual physical or emotional stress, and the health of the horse will be
affected in nearly all body systems. This is just a partial list of the consequences:
*Muscles may waste or weaken
*Tendons and ligaments may weaken or fail to heal properly
*Hooves become prone to abscesses and laminitis
*Fat deposits may form in abnormal places
*Hair growth may increase subtly or dramatically (ie a winter coat all year)
*Skin defenses may decrease leading to infections like rain rot or scratches
*Anhidrosis (failure to sweat appropriately)
*increased thirst and urination
*And general immunity may decrease leading to an increase in risk for any
infectious disease.
Despite all these negative consequences, there is a lot of good news for the horses at
risk for this disease. We can prevent most of these outcomes in most horses by
detecting the disease and starting treatment before you can see the outward signs. We
can reverse some of the effects of the disease and improve the health of horses that
already have obvious signs by starting treatment later in the course of the disease.
Part 2: Diagnosis
In the last 15 years there have been more than a dozen tests commercially available or
discussed in the veterinary literature, so you can imagine that there has been confusion,
even among veterinarians. This information may still continue to change, as there is a
great deal of ongoing research. You or your veterinarian may want to look for resources
from the Equine Endocrinology Group (EEG) or from the American College of
Veterinary Internal Medicine (ACVIM). The information below is based primarily on the
EEG's most current recommendations, at the time of this writing.
How we best diagnose these horses depends on how advanced their disease is at the
time of testing. Very late, untreated disease or cases not responding to treatment can
be diagnosed just by looking at the horse: there is nothing else that causes the very
long characteristic hair coat that is found in advanced PPID. But, it will greatly benefit
your horses to diagnose it much earlier. For more moderate cases, measurement of
ACTH levels in the blood is the best test. While there used to be seasonal restrictions,
recommended fasting, and difficult sample handling for your veterinarian to worry about,
this is no longer true. Current EEG recommendations are greatly simplified, making this
test easier for you and your veterinarian. In the early cases, this simple ACTH test will
come back in the normal range, missing this opportunity to start treatment before
damage is done to the body. Many more of these early cases can be diagnosed with a
thyroid releasing hormone stimulation test (TRH stim). For this test the horse is given a
small dose of the hormone TRH 10 or 30 minutes before the blood sample is collected.
At this time, there are seasonal restrictions for the TRH stim test, but there is also
ongoing research working to solve that problem.
There are a long list of other tests that have been done for this disease. If your
veterinarian offers you a test not discussed here I suggest checking out the chart of
tests on the EEG website. Or use the diagnostic algorithm found at Prascend.com.
The next question is when to test and how often. You have to balance the risk of the
disease with the cost of the test against your center's resources; hopefully your
veterinarian can help you do this. As a rule of thumb, I currently recommend an annual
or at least every other year test during the years that the horse is at risk. For Morgans,
Pasos, Arabians, Mustangs, Andalusians, and all ponies I recommend starting at about
age of 8 years or sooner with a history of laminitis. For all other breeds I recommend
starting at about the age of 15 or sooner with a history of laminitis. Even in breeds that
are not generally high risk, there are some bloodlines that have early onset, don't be
afraid to start testing early if there is a known risk of laminitis or PPID in the bloodline.
Part 3: Treatment
Unfortunately, we do not have a cure for this disease right now. We do have
medications that can keep the symptoms controlled and that dramatically decrease the
biggest health consequences of this disease. In the recent past we had to rely on
custom compounded medications for this disease. The problem is that pergolide, the
best drug for most horses, is really tricky to make in a form that is stable and delivers a
consistent dose. This lead to a lot of treatment failures. However, there is now an FDA
approved formulation of the medication, called Prascend. This medication, given daily,
controls the effects of PPID on the horse's body. It is a tiny tablet that is easy to give
and most horses eat readily in their grain. In the nearly 150 horses I have managed on
Prascend, the only side affect has been a small number of horses with a short term loss
of appetite during the first month of treatment. In a few severe cases high doses of
Prascend may combined with other medications for the best results. Your veterinarian
is the best resource for these cases.
It is important to remember that we are treating the disease, not curing it. The changes
in the pituitary will continue to progress in spite of any medical treatment. This means
that there will be a need to retest every year or two during treatment to be sure that the
treatment is still sufficient. Retesting may also be indicated after a medication or
dosage change.
It is very likely that your veterinarian will mention insulin resistance (IR) or Equine
Metabolic Syndrome (EMS) during the course of evaluation of horses for PPID. EMS
and IR are commonly found in the high risk breeds for PPID, and researchers suspect
that they are, in fact, related pathologies. I find that when PPID is brought under control
first, then EMS and IR are easier to control.
Part 4. Management and myths:
In addition to the diagnosis and treatment already discussed, these horses sometimes
need a little extra thought and care. Due to damage that may have already happened
to their feet, they may need more frequent trimming or corrective shoeing. Be sure to
be extra diligent in foot care! If you are managing a PPID horse that tends toward
remaining over weight despite your best efforts, or with a history of laminitis, you need
to talk to your veterinarian before allowing this type of horse to have access to grass. In
some cases these horses are very thin, again talk to your veterinarian about what kind
of diet is best suited to your patient, as their needs can vary. If their hair coat remains
excessively long and thick despite medication you should both talk to your veterinarian
and get the horse clipped during warm weather. Finally, it is common for horse people
to try to apply what has been learned about small animal vaccination intervals to horses.
Unfortunately, horse vaccine intervals cannot be lengthened, and in horses with PPID,
immune response to vaccines is likely to be even weaker and shorter than I healthy
horses. You need to be extra diligent about regular vaccine intervals for these horses.
Watch for new guidelines for older and PPID horses in the coming years.
Many alternative and complimentary treatments have been proposed for horses with
PPID. The most common one purported to treat the disease is Chasteberry.
Unfortunately, research has proven this one ineffective. I strongly recommend starting
treatment efforts with Prascend in every case of PPID. However, if for any reason your
organization has decided to use any alternative treatment instead of medication, be
sure to retest to check the effectiveness of that treatment! Doing so will protect the
health of your horse and potentially save you money on treatments that do not work.